Insight into the behavior of colloidal gas aphron (CGA) fluids at elevated pressures: An experimental study

Abstract

Recently, colloidal gas aphron (CGA) fluids technology has been employed to drill depleted oil and gas reservoirs. Almost all reported experience on CGA fluids were conducted at ambient conditions, and little attention has been paid on the behavior of CGAs at high pressures which is more close to real conditions. In this study, high pressure experiments were conducted by using High Pressure Microscope cell to visualize/monitor the behavior of CGAs at elevated pressures. Single bubble behavior and bubble size distribution (BSD) of CGAs were investigated under different scenarios of pressure change. Results of experiments revealed that BSD of CGAs is controlled by the path of pressure changes, and sudden pressure change affects BSD less than stepwise changes in pressure. The pressure-volume product of bubbles, as a new criterion for analysis of single bubble behavior was introduced. The behavior of pressure-volume product for a single bubble shows significant loss of air via diffusion through tri-layer film into the bulk phase during compression as well as a hysteretic behavior during compression and decompression processes. Monitoring single bubble behavior at elevated pressures revealed that CGAs meet three distinct regions with time: first, they exhibited a sharp reduction in bubble size (region I), then became stable with minimum change in bubble diameter (region II), and finally, the size of bubbles decreased suddenly and after a short time they were collapsed (region III). Observations which showed aphrons were survived at pressures as high as 2000psig may support the idea for field applications of CGAs as drilling fluids. Results of this work may provide thorough insight into behavior of CGA fluids at elevated pressures.